Copy app bundle file (read-only) to app documents (read-write, database etc).

Database.swift

func copyDatabaseIfNeeded() {

    let fileManager = FileManager.default

    guard let documentsUrl = fileManager.urls(for: .documentDirectory, in: .userDomainMask).first else { return }

    let finalDatabaseUrl = documentsUrl.appendingPathComponent("sample.db")

    do {
        if !fileManager.fileExists(atPath: finalDatabaseURL.path) {
            if let dbFilePath = Bundle.main.path(forResource: "sample", ofType: "db") {
                try fileManager.copyItem(atPath: dbFilePath, toPath: finalDatabaseUrl.path)
            } else {
                print("Database file found at app bundle")
            }
        } else {
            print("Database file found at path: \(finalDatabaseUrl.path)")
        }
    } catch {
        print("Unable to copy database file: \(error)")
    }
}